BRIEF REPORTS

Pulse Oximetry in Cyanotic Congenital Heart Disease Samuel S. Gidding, MD

T ranscutaneous oximetry allows for both noninvasive and continuous assessment of arterial oxygenation.

Transcutaneous oxygen partial pressure (PO$ monitor- ing has been shown to correlate sufficiently well with arterial oxygen pressure to be used clinically in inpatients and outpatients with congenital heart disease and chronic lung disease.’ However, this technique is limited by the nonlinear relation between arterial oxygen pressure and oxygen content created by the oxyhemoglobin dissocia- tion curve and interindividual variability in Pso.~ Pulse oximetry allows for the noninvasive assessment of oxygen saturation, thus improving the ability to estimate oxygen content. Prior studies suggested that although there is a good correlation between transcutaneous and arterial oxygen saturation, this technique can overestimate oxy- gen saturation at lower levels.3-6 Because patients with cyanotic congenital heart disease generally have chronic hypoxemia of greater severity than do those with lung disease, this overestimation may have clinical signifi- cance. We evaluated the reliability of transcutaneous pulse oximetry in patients with congenital heart disease in the cardiac catheterization laboratory and in clinical set- tings to determine the usefulness of this technique in clinical practice.

Children (n = 44) undergoing cardiac catheteriza- tion for a variety of clinical conditions, also underwent continuous transcutaneous monitoring (Nellcor Pulse Oximeter) of oxygen saturation as part of their diagnos- tic study. Directly measured arterial oxygen saturations (n = 66) (Radiometer A/S Copenhagen OSM2 Hemox- imeter) were compared with simultaneous transcutane- ous oxygen saturation readings. Diagnoses that provided additional information concerning the clinical use of the technique beyond the direct comparison included tetral- ogy of Fallot with hypoxemic spells, device closure of fenestration after a Fontan procedure, and right-to-left ductal shunting. Comparisons between arterial and transcutaneous pulse oximetry were performed using paired t tests and linear regression analysis.

Transcutaneouspulse oximetry consistently overesti- mated arterial oxygen saturation (88 f 10% us 84 f 10%; p <O.OOl). Linear regression analysis comparing transcutaneous and arterial oxygen saturation showed a good correlation, but an increasing disparity between transcutaneous and arterial saturation as oxygen satu- ration decreased (Figure 1).

Examples of successful uses include the following: The onset of a tetralogy spell was quickly recognized by observing a sudden decrease in the digital readout of oxygen saturation. Successful occlusion of a right-to- left atria1 level shunt after a fenestrated Fontan proce- dure was also demonstrated initially by an increase in

From the Division of Cardiology, Children’s Memorial Hospital, Northwestern University, 2300 Children’s Plaza, Chicago, Illinois 60614. Manuscript received December 13, 1991; revised manuscript received and accepted February 27,1992.

oximeter saturation. Right-to-left ductal shunt in apa- tient with interrupted aortic arch was demonstrated transcutaneously by increased transcutaneous satura- tion in the right arm compared with in the leg.

The overestimation of arterial oxygen saturation by transcutaneous monitoring has clinical significance. For example, an infant with tachypnea being evaluated for respiratory distress may have transcutaneous saturation of 80 to 85% in room air, which increases to 95 to 98% in high oxygen. However, because of the overestimation of arterial oxygen saturation, the clinician may be falsely reassured that the infant does not have an intracardiac right&to-left shunt, unless a transcutaneous PO2 is also measured. In an outpatient with cyanotic congenital heart disease, a transcutaneous oxygen saturation of 80% would predict an estimated arterial saturation of 71 to 79%. The lower end of this range may suggest the need for clinical intervention, whereas the upper end would be considered adequate.

This study showed that transcutaneous oximetry ap- proximates arterial oxygen saturation well enough to be used clinically, but overestimation of oxygen saturation is likely, particularly at lower saturations. The regression equation obtained in this study relating transcutaneous to arterial oxygen saturation is similar to those obtained in nurseries, other pediatric studies and during general anes- thesia.3-6 We used transcutaneous oxygen measurements in conjunction with a complete blood count to successful- ly assess oxygen content in outpatients with cyanotic con- genital heart disease and chronic lung diiease.137

Regression Line Lineof Identity l

/

Tc02Sat =0.9(Art 02Sat)+l4

FIGURE 1. Relation between tranwcutaneous (T,) and dii moaswod artdai (Art) oxygen (02) saturation (Sat) in 44 pa- tiOlltS(66 memu-). Regressh linofortdaiionbo- twooa iranscutanesus and arkriai oxygen saturti is shown.DiRomcobotw~~linoandiine!ofiderrtity roGect8 dogreo of overestimation of arterial oxygen saturation.

BRIEF REPORTS 391

We recommend the use of pulse oximetry for monitor- ing oxygen content in cyanotic patients if the potential overestimation of oxygen saturation is considered, and a hemoglobin is measured to calculate content.7 Both mea- surements are necessary, because a cyanotic patient with- out an appropriate increase in hemoglobin concentration will not have adequate oxygen delivery and will be at risk for stroke. We previously published normal values for hemoglobin based on degree of hypoxemia for prepuber- tal children.7

Admowledgmenb We would like to thank laborato- ry technicians Linda Gulian-Andrews, Delia Mendoza, Stacey Snowden, and Robert Zwinak, who collected data for this study, and Shann Bulger for secretarial assis- tance.

1. Gidding SS, Moorehcad C, Rosenthal A. Tramcutaneous oxygen monitoring in the management of outpatients with congenital heart defects. Am JDis Child 1985;139:288-291. 2. Berman W Jr, Wood SC, Yabek SM, Dillon T, Fripp RR, Burstein R. Systemic oxygen transport in patients with congenital heart disease. Circulation 1987;75:360-368. 3. Ridley SA. A comparison of two pulse oximeters. Assessment of accuracy at low arterial saturation in paediatric surgical patients. Anesthesia 1988;43: 136-140. 4. Southall DP, Bignall S, Stebbens VA, Alexander JR, Rivers RP, Lissauer T. Pulse oximeter and transcutaneous arterial oxygen measurements in neonatal and paediitric intensive care. Arch Dis Child 1987;62:882-888. 5. Bossi E, Meister B, Pfenninger J. Comparison between tramcutaneous PO2 and p01 for monitoring 02 treatment in newborns. Adu Exp &fed Biol 1987;220: 171-176. 6. Jennis MS, Peabody JL. Pulse oximetry: an alternative method for the assess- ment of oxygenation in newborn infants. Pediatrics 1987;79:524-528. 7. Gidding SS, Bessel M, Liao Y. Determinants of hemoglobin concentration in cyanotic heart disease. Pediatr Cardiol 1990;11:121-125.

Effects of Homograft Blood Type and Anatomic Type on Stenosis, Regurgitation and Calcium in Homografts in the Pulmonary Position Robert E. Shaddy, MD, Lloyd Y. Tani, MD. Jane E. Sturtevant, BSN, Linda M. Lambert, RN, and Edwin C. McGough, Mb

T he use of both aortic and pulmonary homografts in the pulmonary position for treatment of right ven-

tricular or pulmonary outflow tract obstruction has gained widespread popularity.1-3 Although this homo- graft tissue presents a potential allogeneic stimulus to the recipient, little is known about the effects of blood-type (ABO) compatibility or incompatibility on homograft function.4 This study retrospectively reviews the outcome of homografts in the pulmonary position in 39 consecu- tive children who had placement of an aortic or pulmo- nary homograft in the pulmonary position for treatment of pulmonary outflow tract obstruction.

Between February 1987 and September 1990, 48 children at Primary Children’s Medical Center under- went surgical placement of an aortic or pulmonary ho- mograft in the pulmonary position for treatment of pul- monary outflow tract obstruction. There were 7 early (<30 days after surgery) and 2 late (3 to 6 months after surgery) deaths. The remaining 39 patients (mean age 5.8 f 4 years, range 3 months to I7 years; weight 18 f 12 kg at time of surgery) constitute this study. Twenty-two patients had pulmonary stenosis or atresia with ventric- ular septal defect, 8 had truncus arteriosus, 7 had pul- monary stenosis with D-transposition of the great arter- ies, and 1 had pulmonary atresia with intact ventricular septum. Additional procedures performed at the time of surgery included closure of the ventricular septal de- fect in 34 patients, arterial switch procedure in 2, and aortic valve replacement, atria1 baffle procedure and Glenn procedure in 1 each; No attempt was made to prospectively ABO match the homograft to each patient at the time of surgery, and the decision to use either an aortic or pulmonary homograft was based solely on availability at the time of surgery.

From primary Children’s Medical Center, Salt Lake City, Utah 84113, and the University of Utah, Salt Lake City, Utah. Manuscript received December 2,199 1; revised manuscript received and accepted March 5, 1992.

Fourteen patients had an identical homograft ABO match, IO had a compatible but not identical ABO match, and 15 had an incompatible ABO match. Com- plete 2-dimensional and Doppler ultrasound examina- tions were performed 20 f 15 months after surgery. Doppler estimates of homograft stenosis were performed with blind and 2-dimensional directed continuous-wave Doppler recordings measuring the maximal gradient de- tected along the conduit. Pulsed and color Doppler esti- mates of homograft regurgitation were performed and quantitated, as previously described by Meliones et al.’

There were no significant differences between ABO groups with regard to the degree of homograft stenosis, or the presence of conduit regurgitation, which was ei- ther absent (n = I5), mild (n = II), moderate (n = 12) or severe (n = 1) (Table I). Similarly, the incidence of radiographic calcification detected at 14 f 9 months (range 3 to 29) after surgery was not signij?cantly differ- ent between ABO groups (Table I). There were I3 aortic and Mpulmonary homografts. The Doppler estimate of the maximal peak systolic pressure gradient across the homograft was not significantly different between aortic (31 f 28 mm Hg) andpulmonary (19 f 16) homografts (p = 0.10). Similarly, the percentage of patients in each group with homograft regurgitation was not significant- ly different between aortic (77%) and pulmonary (58%) homografts. However, radiographic calcification of the homograft was seen more frequently in patients with

TABLE I Homograft Stenosis, Regurgitation and Calcium in Identical, Compatible and Incompatible Blood-Type Matches

Identical Compatible Incompatible

Stenosis (pressure gradient)

(mm Hg)

22 2 5 25 f 8 19 f 4

Regurgitation Calcium (n) (%) (n) (%)

6 (421 3 (21) 8 (80) 2 (20)

10 (67) 5 (33)

392 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70 AUGUST 1, 1992